particles time to be handled in frames instead of seconds optionally

code/entities/particle.lua

@@ -21,8 +21,14 @@ function Particle:new(x,y,particle_data)
 	o.sprite_flip = particle_data.sprite_flip or o.sprite_flip
 
 	o.time = particle_data.time or nil
-	if o.time ~= nil then o.time = o.time * game.framerate end
-
+	if o.time ~= nil then
+		if particle_data.time_unit ~= nil
+		and particle_data.time_unit == "frames" then
+			o.time = o.time
+		else
+			o.time = o.time * game.framerate
+		end
+	end
 	o.timer = 0
 
 	o.vel = {